People said the same about Lennox Lewis till he beat Mike Tyson to a pulp, smacked Holyfield twice (though the first one was an American job and fictitiously ruled a draw), and whooped Vitali before retiring as the undisputed heavyweight champion of the world.
Tyson has suspect defence and he never fought past the fight 6 round. The man didn't even beat any top heavyweight boxer in his prime and the biggest name on his resume was a flabby, old, and sick Larry Holmes that didn't box for two years. And he also dodged Riddikk Bowe. Yes, Tyson was explosive and he was fun to watch but he wasn't invincible and he lost to all the top fighters he fought.
Wilder would be an easy fight. The man has no jab, zero angles, no head movement and he relies only on his big right, apart from throwing wild punches like an amateur. Once Josh takes his big right away - he's going to get punch drunk and throw in the towel.